The present invention relates generally to electrical heating systems for footwear, and specifically to a universal heating system adaptable to ski boots of any design and manufacture.
Cold, and specifically cold feet, has been a major limiting factor in the ability of the outdoor sportsman to appreciate and enjoy winter sports. As technology has improved throughout the years, fleece-lined leather boots have given way to footwear constructed using various synthetic shell materials and foam, Thinsulate.TM. and other insulations. This improved winter footwear has benefited skiers, who now enjoy a variety of rigid boot shell designs insulated with the aforementioned materials. However, since downhill or alpine skiers spend extended periods of time outdoors, two major problems still inhibit foot warmth, one being a function of the nature of the sport and the second of advances in boot technology. The first phenomenon referred to above involves the long periods of relative inactivity while skiing, attributable to lift lines and long lift rides, the latter on chair lift chairs which inhibit blood circulation to the lower extremities. The second phenomenon is associated with boot technology advances in the areas of foot retention and responsiveness of the boot and attached ski to body movement. Even though many different lasts are available for ski boot inner shells, and custom lasts are relatively inexpensive for the benefit gained, many skiers tighten their boots to an extraordinary degree to give better ski control and feedback from the ski through the foot, ankle and calf regions of the leg. This tightness constricts the foot and ankle regions, restricting blood flow thereto and contributing to cold feet.
Ski racers, like other skiers, experience the above-mentioned problems. However, the adverse consequences of cold feet to their performance is even more dramatic at high racing speeds where the "feel" of the skis and terrain is all-important to promote optimum times and avert catastrophic injury.
Since completely insulated ski boot structures would be massive and unwieldy, many efforts have been made to artificially provide heat, generally electrical, to the feet. For example, U.S. Pat. No. 4,080,971 discloses a calf-mounted battery pack having a wire extending to a footwear insole incorporating a resistance heating element. This device is obviously inappropriate for skiing, as the bumps and shocks encountered as well as calf flexing would cause the battery pack to slip down the leg in short order. U.S. Pat. No. 4,837,494 discloses a ski-mounted battery pack including a wheel-type generator for battery recharging, the battery pack providing power to a resistance element in a ski boot through a connecting cable. The battery pack and generator weigh down and unbalance the ski, and the presence of cable connectors is a safety hazard to proper binding operation and to a total boot from ski release.
Several designs have been proposed for incorporating batteries in the ski boot structure itself. U.S. Pat. Nos. 3,977,093 and 4,507,877 each disclose batteries housed in boot or shoe soles, powering resistance heater type insoles. These designs render it virtually impossible to remove and replace batteries during a day of skiing, and additionally require specialized footwear designs having battery cavities. Additionally, the on/off switch of the '093 patent is inside the boot and activated by the heel of the wearer, preventing its being turned off. The '877 switch is on the exterior of the boot, and thus susceptible to water incursion and icing problems, as well as impact damage from skier falls.
U.S. Pat. No. 4,798,933 discloses another design, one of the type commonly seen in commercially-available heated ski boots today. This design uses a molded cavity in a bulge on the back of the ski boots to accommodate batteries, but there is no access to remove same except from the inside of the boot after the inner bladder or soft shell is removed. Again, as with the designs previously mentioned, the on/off switch is on the exterior of the boot.
U.S. Pat. Nos. 4,697,359 and 4,780,968 disclose several variations of a ski boot design with integral heater, wherein a plug-in type battery pack is housed in cavities or apertures which can be located on the back, instep or top front of the boot. The '359 patent discloses a battery pack having only contacts for plugging into the boot, the switch for turning the current on or off being included in the boot structure. The '968 embodiment includes the switch in the battery pack. The disadvantage of the foregoing designs resides in the necessity of special boot shells to accommodate the battery packs, and of fragile switches susceptible to icing as the boots become wet and then freeze during wear.
A more versatile boot heater design is disclosed in U.S. Pat. Nos. 3,859,496 and 3,946,193, wherein a battery case is mounted on the heel or back of a ski boot having a metal mounting plate thereon, and the heater is turned on and off by moving the battery pack up and down on the mounting plate on rails between an on and an off position. While this design is usable on any ski boot to which a mounting plate has been affixed, the use of electrical contacts on the exterior of the battery pack can result in shorts from water on the mounting plate or battery pack, and the boot wearer has to ascertain whether the heater is on or off by experimentally sliding the packs up or down on the plates, waiting to see if his feet get warm, or having a companion switch to turn the device on or off or observe which position the pack is in on the plate. Moreover, the mounting plate is itself mounted on a bracket secured to the ski boot, leaving the wires to the contacts exposed to the weather as well as build up of water, snow and ice, which accelerates deterioration thereof. Finally, the heating element is electrically connected to the mounting plate contacts via screws accessible only from the boot interior, making easy removal of the insole or boot liner impossible.
In short, the boot heaters of the prior art suffer from either reliability problems, operational problems, or manufacturing complexities which render them all inadequate in solving the problem of cold feet in an economical, reliable manner.